The present invention relates to adjustment mechanisms for sighting devices such as riflescopes and, in particular, to a non-telescoping adjustment mechanism, including a scale that indicates the number of rotations of the adjustment mechanism.
Riflescopes have long been used in conjunction with firearm, such as rifles and handgun to allow a shooter to accurately aim the firearm. Because bullet trajectory, wind conditions, and distance to the target can vary depending upon shooting conditions, quality riflescopes typically provide compensation for variations in these conditions by allowing a shooter to make small adjustments to the optical characteristics or the aiming of the riflescope relative to the firearm on which it is mounted. These adjustments are known as holdover (also called xe2x80x9celevationxe2x80x9d) and windage, and are typically accomplished by lateral movement of an adjusting member, such as a reticle located within the riflescope, as shown in U.S. Pat. No. 3,058,391 of Leupold, or pivotal movement of lenses mounted to a pivot tube within a housing of the riflescope to divert the optical path of the observed light before it reaches the reticle, as shown in U.S. Pat. Nos. 3,297,389 and 4,408,842 of Gibson. In these designs, a shooter accomplishes adjustment of windage and holdover by way of two laterally protruding adjustment knobs or adjustment screws, typically extended at right angles to each other, that are operatively connected to the adjusting member. A spring located between the housing and the adjusting member opposite the adjustment knobs biases the adjusting member against the adjustment knobs so that the adjusting member follows the movement of plunger screws of the adjustment knobs. The adjustment knobs may be sealed to the housing to maintain a nitrogen gas charge within the interior of the housing to prevent fogging and condensation on internal lens surfaces. The plunger screws typically include very fine threads and the adjustment knobs are rotatable through multiple rotations to allow precise adjustments.
An index mark on the housing of the riflescope provides a reference by which a shooter may read a scale marked around the circumference of the adjustment knob. The shooter typically adjusts windage and elevation so that a bullet will hit a target at a particular known reference distance, e.g., 100 yards, when an aiming mark of the reticle is centered on the target viewed through the riflescope. This process is known as xe2x80x9csighting in.xe2x80x9d When the shooter wants to shoot at a target at a different distance, e.g., 200 yards, or under different wind conditions, the shooter rotates the holdover and windage adjustment knobs a known amount to accurately place the aiming mark for the target. Some scopes provide a mechanism for adjusting the angular position of the scale on the knob independently of the actual windage or holdover adjustment so that the shooter can align the zero mark of the scale with the index mark on the outer tube after the rifle has been sighted in at the reference distance. The shooter can then easily return to the sighted-in windage and holdover positions. However, a scale around the circumference of the adjustment knob only indicates rotation of less than 3600 and does not provide the shooter with an indication of the number of rotations of the knob.
Some adjustment mechanisms are telescoping, i.e., they extend along their axis of rotation as they are rotated. U.S. Pat. No. 2,165,796 of Humeston describes such an adjustment mechanism that extends outwardly from the riflescope and that includes a cup-shaped cap having an inwardly depending skirt. The cap, which drives an adjustment screw, is manually rotatable about a cylindrical sleeve having transverse markings along its length. As the cap is rotated, it moves/extends longitudinally with the adjustment screw so that an inward edge of the skirt moves along the transverse markings on the sleeve to indicate the number of rotations. A click mechanism comprising a detent post, around which a detent finger of the cap rides, provides an audible or tactile indication for every increment of rotation of the cap. The shooter thus need not take his or her eye from the target to make fine adjustments to windage or holdover. Telescoping adjustment mechanisms of this type are not easily sealed to the housing of the riflescope. Furthermore, when extended, they tend to catch on clothing of the shooter, on vegetation, or other protruding items and are thus easily damaged. Further, because the adjustment screw is directly connected to the cap, the amount of longitudinal movement of the adjustment screw per rotation of the cap determines the desired spacing of the transverse markings. If the adjustment screw includes very fine threads to allow minute adjustments to windage and holdover, the longitudinal movement of the screw and cap will be so small, and the transverse markings so closely spaced, that it will be difficult to determine the exact number of complete rotations by viewing the position of the edge of the cap along the transverse scale.
In many of the prior art aiming devices, a rotating adjustment screw bears directly on the adjusting member. Any out-of-roundness of the bearing end of the adjustment screw will cause undesirable fluctuations in the sighting of the aiming device. Any roughness or non-planarity of the bearing end of adjusting member will cause deviations in the sight""s aim as the adjustment screw is rotated and different regions of its bearing end press against the adjusting member. Moreover, friction between the rotating adjustment screw and the adjusting member can cause wear on both parts where they contact. Such wear can further degrade the performance of the adjustment mechanism and can cause small particles to dislodge and affect the optics of the riflescope.
Many prior art adjustment knobs are also permanently installed in a housing of the riflescope and cannot be changed in the field without damaging the riflescope or breaking the gas-tight seal that maintains a nitrogen gas charge within the housing.
A need exists for an improved adjustment mechanism that allows a shooter to easily and accurately determine the extent of adjustment through multiple rotations of the mechanism by way of a scale on the exterior of the mechanism, while maintaining an optimal length of the mechanism for gripping and for viewing of the scale.
In accordance with the present invention, a non-telescoping adjustment mechanism is provided for making adjustments in a riflescope or other aiming or sighting device, such as a laser sight or theodolite. In a preferred embodiment, a riflescope with a non-telescoping adjustment mechanism includes a housing having an interior and an exterior, and an adjustable member that is movably mounted within the interior of the housing for making elevation and/or windage adjustments to the aim of the riflescope. The adjustment mechanism includes a core that is rotatable about a central axis of rotation of the adjustment mechanism and supported by the housing, an adjustment plunger that is threadably coupled to the core, and an adjustment knob. To adjust the adjustment mechanism, the shooter turns the adjustment knob. The core is rigidly connected to the adjustment knob for rotation therewith and restricted from moving along the axis of rotation relative to the housing of the riflescope. Rotation of the core causes the adjustment plunger to move relative to the core along the axis of rotation, thereby operatively engaging the adjustable member and causing the adjustable member to move. The adjustment mechanism extends through an opening of the housing to operatively engage with the adjustable member within the housing, while being manually adjustable from outside the housing.
Upon rotation of the adjustment knob (and the core therewith), the adjustment plunger extends within the interior of the housing through an opening, without changing the distance by which the adjustment knob protrudes from the housing (i.e., a non-telescoping adjustment, externally). A gas-impermeable seal surrounds the opening of the housing and is positioned between the housing and the core to seal the interior of the housing, thereby preventing fogging and condensation on optical surfaces within the housing. In an alternative embodiment, the core and plunger are reversed so that the core extends within the interior of the housing through the opening in response to rotation of the adjustment knob, thereby causing movement of the adjustable member. In such an embodiment, the gas-impermeable seal may be positioned between the housing and the adjustment plunger.
An index slide is threadably coupled to the adjustment knob and slidably guided along a longitudinal slot for movement, along a slide path that extends along the axis of rotation between the adjustment knob and the core, in response to rotation of the adjustment knob. In a preferred embodiment, the index slide is a tube that is keyed, either directly or indirectly, to a slot in the housing or another non-rotating component of the adjustment knob, to thereby rotationally restrict the tube, causing it to move along a substantially linear path along the axis of rotation in response to rotation of the adjustment knob.
When the shooter adjusts for windage and holdover, a datum, such as the inwardly depending edge of the adjustment knob, moves along a scale, which may include a set of indicia positioned on the index slide and spaced apart along the axis, for example. The direction of relative movement of the scale and the datum is along the axis of rotation. The scale and the datum cooperate so that their relative movement provides a visual indication of the amount of rotation of the core, such that the shooter can determine the number of turns through which the adjustment mechanism has been rotated.